Cryogenic Semiconductor Amplifier for RSFQ-Circuits With High Data Rates at 4.2 K

Wuensch, S.; Ortlepp, T.; Crocoll, E.; Uhlmann, Friedrich; Siegel, M.

doi:10.1109/tasc.2009.2018425

Cited by 11 publications

(4 citation statements)

References 5 publications

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“…From the measured resonance frequencies and dimensions of the parallel plate capacitors we extract the value of the relative permittivity to be ε r = 5.7, suggesting that the stoichiometry of the film is close to silicon monoxide SiO. We employed a broadband cryogenic HEMT amplifier (20 MHz -12 GHz) 18 and a power combiner with a bandwidth ranging from DC to 12 GHz, serving here as a broadband alternative to a circulator. Its transmission properties are illustrated in Fig.…”

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confidence: 99%

Probing the density of states of two-level tunneling systems in silicon oxide films using superconducting lumped element resonators

Skacel

Kaiser

Wuensch

et al. 2015

Applied Physics Letters

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We have investigated dielectric losses in amorphous SiO thin films under operating conditions of superconducting qubits (mK temperatures and low microwave powers). For this purpose, we have developed a broadband measurement setup employing multiplexed lumped element resonators using a broadband power combiner and a low-noise amplifier. The measured temperature and power dependences of the dielectric losses are in good agreement with those predicted for atomic two-level tunneling systems (TLS). By measuring the losses at different frequencies, we found that the TLS density of states is energy dependent. This had not been seen previously in loss measurements. These results contribute to a better understanding of decoherence effects in superconducting qubits and suggest a possibility to minimize TLS-related decoherence by reducing the qubit operation frequency.PACS numbers: 85.25.Cp, 77.22.Gm, 74.50.+r, 73.61.Jc For the realization of a quantum information processor based on superconducting circuits, physical mechanisms responsible for decoherence have to be cleared up 1 . Microwave resonators are key ingredients of superconducting quantum circuits. Dielectric thin films are widely used in qubit fabrication as insulating layers and overlay capacitors of the resonators. Lumped capacitors are often employed in qubits to shunt Josephson junctions in order to adjust their operation frequency. It is well established 2 that two-level tunneling systems (TLS) in insulating films contribute to dielectric losses at microwave frequencies and thus often appear as dominant decoherence sources, in particular for superconducting phase qubits. In this paper, we experimentally study microwave properties of amorphous dielectric thin films embedded in superconducting lumped element resonators.Dielectric losses induced by TLS in the qubit working regime have been extensively studied in recent years and good agreement with the predictions of the TLS tunneling model has been found 2-6 . However, most of the investigations were done using coplanar waveguide resonators, where TLS and thus losses originate from surfaces 3-6 . The bulk losses in dielectric films may also play a significant role for a variety of qubit designs and till now remain less understood. Furthermore, there is little known about the energy dependence of the TLS density of states n(E) in typical qubit materials. A better understanding of this matter would allow to improve qubit coherence and lead to a better qubit design and operation. In the standard tunneling model (TM) of glasses, a dependence of n(E) on energy is not excluded 7 , but characteristic glassy behavior refers to an essentially constant density of states 8,9 . So far, a slight dependence of n(E) on energy had been extracted from specific heat measurements 10 , but could be explained in terms of the TM taking into account the time scales of the measurements 7 . Earlier investigations of the sound velocity in glassy thin a-SiO x films in the kHz 11 and 300 MHz 12 ranges validate the constancy of the den...

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confidence: 99%

Probing the density of states of two-level tunneling systems in silicon oxide films using superconducting lumped element resonators

Skacel

Kaiser

Wuensch

et al. 2015

Applied Physics Letters

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“…During the measurement the sample was biased with a DC current from a low-noise current source. The response to the IR radiation was amplified by a two-stage low noise amplifier (20 dB gain), which was especially designed for cryogenic applications [15]. After amplification, the signal was feeded out to a spectrum analyzer by a rigid stainless steel coaxial cable and a vacuum feed-through.…”

Section: Photo Responsementioning

confidence: 99%

Infrared Photo-Response of Fe-Shunted Ba-122 Thin Film Microstructures

Rehm

Henrich²,

Hofherr³

et al. 2013

IEEE Trans. Appl. Supercond.

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We present a study of the response to pulsed infrared radiation of Fe-layer shunted pnictide thin film microstructures. The thin film multilayer consisting of 20 nm thick Fe-buffer, 50 nm thick Ba(Fe,Co) 2 As 2 film and gold protection layer were deposited on heated MgO and MgAl 2 O 4 substrates by pulsed-laser deposition. The multilayers were patterned into 5 to 8 µm wide and 5 µm long microbridges by electron-beam lithography and ion-milling technique. The microbridges show T c ≈ 20 K and a critical current density up to 2.56 MA/cm 2 at T = 10 K. The photo-response of Fe-shunted Ba(Fe,Co) 2 As 2 thin film microbridges to infrared radiation was studied in a wide range of incident optical power, operation temperature and bias current. We have found that the electron energy relaxation in studied multilayers is dependent on substrate material and is 1.75 times faster in case of MgAl 2 O 4 characterized by lattice matching to pnictide film in comparison to MgO substrate.Index Terms-barium compounds, high temperature superconductors, infrared detectors, superconducting photodetectors.

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“…The number of Josephson junctions is a compromise between the targeted output voltage on one side and the operation stability and circuit complexity on the other side. The smallest version with only two junctions has proven to operate very stably as a synchronous digital voltage doubler [16,17].…”

Section: Introductionmentioning

confidence: 99%

Design guidelines for Suzuki stacks as reliable high-speed Josephson voltage drivers

Ortlepp

Zheng

Whiteley

et al. 2013

Supercond. Sci. Technol.

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The application of superconducting circuits for high-performance computing and high-speed analog-to-digital converters suffers from the difficulty of amplifying the weak signals of superconducting circuits to the volt level of semiconductor electronics. We refer to the most accepted Josephson circuit used to amplify weak signals of about a millivolt to several tens of millivolts as a Suzuki stack. It can be directly triggered by a single flux quantum pulse and has a very high switching speed of about 25 ps.We report here an in-depth study of design issues for Suzuki stacks with extensive systematic simulations as well as experimental results. We explain the origin of previously reported phenomena such as multiple-level switching, high bit-error-rates, and interactions between stacks, and give design guidance for avoidance of such problems. We show experimental results for a set of Suzuki stacks operating correctly and independently with a single power supply.The presented design guidelines address important characteristics that need to be optimized: output voltage, bias margins, operating frequency, bit-error-rate, delay, power dissipation, and physical size.

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Cryogenic Semiconductor Amplifier for RSFQ-Circuits With High Data Rates at 4.2 K

Cited by 11 publications

References 5 publications

Probing the density of states of two-level tunneling systems in silicon oxide films using superconducting lumped element resonators

Probing the density of states of two-level tunneling systems in silicon oxide films using superconducting lumped element resonators

Infrared Photo-Response of Fe-Shunted Ba-122 Thin Film Microstructures

Design guidelines for Suzuki stacks as reliable high-speed Josephson voltage drivers

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